Field of the Invention
This invention entails a novel technique for making extremely fine and uniformly-sized cell structures in light weight, fabricated foam products of certain gas- or vapor-incorporating expandable thermoplastic organic polymer compositions, particularly those of lightly-crosslinked styrene polymers (notably so-modified homopolystyrene) that utilize various imbibed fluorochlorocarbons, and/or hydrocarbons as blowing agents.
Closed-cell foam and the like expanded cellular bodies and products of any of a large variety of thermoplastic polymers which have fine cell structure characteristics and markedly low bulk density are well known materials which are finding ever-increasing use for insulation, packaging, constructional, decorative and many other purposes. U.S. Pat. No. 3,272,215 incorporated by reference thereto, aptly illustrates technology established to such end.
It is well known that lightly-crosslinked thermoplastic polymers will expand to low density foams when impregnated so as to contain effective, expanding quantities of normally-gaseous and/or otherwise relatively volatile blowing agents. Copolymers of styrene with minor amounts of divinylbenzene, such as those which contain on the order of about 0.04 or so percent by total molecule weight of interpolymerized divinyl benzene, are typical of such lightly-crosslinked polymer systems; this being the case when homopolystyrene is the involved polymer. Equivalents as to both involved polymer and involved crosslinking agent are likewise well known and readily available to those skilled in the art.
Fine cells have diameters in the general range of 0.02 millimeters while coarse cells are in the range of 0.18 millimeters and generally acceptable cells are in the range of 0.08 millimeters.
Relevant art representative of the state thereof is representative and brought forth by U.S. Pat. Nos.: 2,848,427; 2,848,428; 2,948,664; 2,948,665; 2,952,594; 3,098,832; 3,264,272; 3,526,652; 3,717,559; 3,878,133; 3,940,517; 3,986,991; and 4,169,921. The disclosure of each being incorporated by reference.
When expandable thermoplastic polymer masses are blown into cellular fabricated foam bodies intended to have extremely fine-sized cells that are desirably uniformly contained throughout the expanded mass, difficulties and unwanted results are frequently experienced in and as a result of the operation. When heretofore known processing techniques for incorporating blowing agent within polymer mass intended to be expandably-transformed including conventional steps associated therewith are utilized, the resultant expanded and foamed body obtained is oftentimes objectionably deficient in both physical property and appearance characteristics in that it does not have optimumly desirable uniform fine-sized cell structure(s) in the very low bulk density product(s) contemplated for preparation. This, of course, handicaps and detracts from the attractiveness and functional utility(ies) wanted for such end products.
It would be advantageous, and it is the principle aim and objective of the present invention, to provide an expedient and easily-accomplished technique for providing expandable foam product raw materials from lightly-crosslinked thermoplastic organic polymer compositions imbibed with certain blowing agent components with the capability of readily being convertible in ordinary expansion transformation operation (as by subjection to heat at an elevated "blowing temperature" with or without physical molding confinement(s)) into excellently-propertied, most attractively-appearing and uniformly fine-celled and structured, very low bulk density and markedly light weight expanded cellular or foamed plastics products.
These benefits and other advantages are achieved in accordance with the present invention; the specific manner of which the same may be accomplished is better understood from a consideration of some preferred forms of same which is hereinafter described in the following claims--all of which for purposes of instant disclosure are here repeated and incorporated by reference.